If only 442 still meant a high-performance Cutlass...

My '98 Jimmy has been a compendium of common Blazer problems: intake gaskets, ball joints, P1870, transfer case seals, HVAC controls, etc. It should have been donated to the Blazer Forum Technical Institute for students to learn how to diagnose and fix common problems on S/T Series trucks.

Now I'm down to the smaller things that don't affect day-to-day driveability. I've got code P0442. It has come up and gone away intermittently over the past six months. During that time I wasn't always driving it (frequently I was fixing it) so I would often clear the code with my scanner. Now that I'm actually driving it regularly the code has become constant and hasn't cleared through regular driving.

The first thing I did was swap the gas cap with the one from my wife's 2000 Blazer. I drove it that way for a couple weeks and the code didn't come back so I bought a new gas cap. The code came back after a couple days of driving with the new cap.

I inspected the lines going into the canister in the rear fender and I didn't see any obvious failures like cracks. I also checked the fuel filler neck as well as I could and didn't see any problems there. I didn't get a very good look at it from where I was at.

I have the factory shop manual and followed as much of the diagnostic procedure as I could. Since I don't have a scan tool that can command the various solenoids and valves to open and close I couldn't get too far. I put a hand vacuum pump on the vacuum line at the intake manifold but I couldn't pull any vacuum on that line.

How do I find the source of the vacuum leak without having a scan tool? I don't know how to complete the tests without a way of manually commanding the valves and solenoids as described in the testing procedure. Any ideas?

 

Toby, this might help. Not sure if its the right one.

 

P0442 is a "small leak" in the EVAP system. Small leak is defined as a leak .030" or smaller. Without a doubt, the most difficult DTC to troubleshoot. It's next to impossible to find the leak without a smoke machine and a capable scan tool. I have a capable scan tool, but no smoke machine, and fought that same battle for a while as well. Ended up removing the steel filler neck. Couldn't see a problem, even with the neck in front of me on the bench. Sealed it off and applied vacuum.... wouldn't hold. Installed a new neck, problem gone. Just a suggestion 2 door filler necks are under $40, 4 door necks are substantially more.

 

This Jimmy is like a master class in Blazer repair. This must be my graduation exam!

Sounds like this may be a good candidate for throwing parts and hoping. Before I replace the filler neck I should probably disconnect the vacuum lines and verify that there are no leaks.

Thanks for the insight. I always appreciate your input Cap'n!

 

There's a ton of vapor lines and seals and places it can leak. It isn't a bad job getting the filler neck out on a 2 door. Remove the left rear wheel, and one plastic shield, there's plenty of room Item Details Pretty simple to check it, kinda "back alley", but it works: Put the palms of your hands over each end of the neck and suck on the vent tube. If it doesn't hold vacuum, ya need a new filler neck. I've found several bad ones on 98 and older recently, the 99's aren't far behind

EDIT: If you end up using the Dorman neck, you'll need a filler cap for a 95 or older with a screw on style cap, (the 98 OEM cap will not fit).

 

just to add my .02$ worth, My fix ended up being the hase clamps on the fuel filler neck were not tight enough, and also needed to replace the screw type clamps, this is after i replaced everything,and i mean everything...

 

Thanks for all the info. Mine is a four-door Jimmy so I'm thinking it's going to be a little bit bigger job than the two-door. Also, I now have a better idea of what to double-check when I get under the truck next.

I did look at the Spectra complete replacement neck for the four-door trucks. It's cheaper than the Dorman. Any thoughts about the Spectra replacement?

 

Not much they can screw up on a filler neck, either one should be fine. Don't forget to check Amazon, Ebay and Rock auto.

 

I always shop around. I found the best price + shipping on RockAuto so if I do end up needing the replacement I'll get it from them.

 

UPDATE: I removed the filler neck and tested it as you described. It holds vacuum and pressure depending on which way I test it. I even put the gas cap on and tested it and it holds both pressure and vacuum.

I also received a replacement filler neck from Rock Auto and it's too short. Apparently "four-door with 18-gal tank" doesn't fit my truck even though it's a four-door with an 18-gallon tank.

I'm thinking the next step is to clean up the original neck and re-install it making sure all the clamps are tight. But after that, then what? Start checking the various vacuum lines? Does the canister itself ever leak?